β2 Adrenergic receptor agonists are recognized as effective drugs for the treatment of pulmonary diseases such as asthma and chronic obstructive pulmonary disease (including chronic bronchitis and emphysema). β2 Adrenergic receptor agonists are also useful for treating pre-term labor, and are potentially useful for treating neurological disorders and cardiac disorders. In spite of the success that has been achieved with certain β2 adrenergic receptor agonists, current agents possess less than desirable potency, selectivity, speed of onset, and/or duration of action. Thus, there is a need for additional β2 adrenergic receptor agonists having improved properties. Preferred agents may possess, among other properties, improved duration of action, potency, selectivity, and/or onset.